A/C cold in rear, meh up front

Last fall I finally fixed my A/C in my 04 suburban. It was a leak in the rear lines, that then turned into a damaged evaporator and rear line. I replaced the evaporator, all the rear lines and the tx valve on the evaporator.

A fellow grm'r recharged the refrigerant and thought thought the pressures were too high, but he was a Nissan tech and not familiar with gm's. Since then the A/C works, but maybe not perfect.

The rear A/C is blowing ice cubes from the rear system, but only cool, bit cold from the front (where I would like it to be better). I don't have any temp numbers, but I can get them. Any ideas? Possibly, the stepper motors on the hvac system that are notorious for being troublesome on this Era GM trucks? Any help would be greatly appreciated.

Thanks,

Chris

Could be a blend door issue, although I haven't seen a GM blend door motor failure that wasn't a phenomenally annoying click/buzz as the blend door motor gears lost mesh and the HVAC control head kept trying to move the motor.

I am trying and failing to remember if GM used H-blocks on their dual A/C units. Can look it up tomorrow if another GRM'er doesn't post up first. Good rear A/C and poor front A/C (or vice-versa) is a common theme on Chryslers when an H-block fails. Can't count how many I've done over the years.

Crimp (gently) one of the heater lines closed and see if the interior temps go down. Or, if the engine is already cold see if the vent temps go up as the engine goes up.

What's an H block?

I thought rear ac systems were a whole separate unit mounted in the cargo area?
Front is the standard underhood car unit while the rear is more like an electric home unit with its guts in the cargo hold.

Sound to me like the underhood version has troubles and the cargo unit is working well.

As far as I know it's all one system with two separate evaporators. I know the lines that go to the rear tie into the lines for the front system.

Mazdax605 wrote: As far as I know it's all one system with two separate evaporators. I know the lines that go to the rear tie into the lines for the front system.

This. It all comes from one compressor with one charge of freon, so if the rear is cold its not a charge problem. Start by removing the cabin air filters. They are under the dash on the passenger side. If it works good without them they are plugged and need replaced. If still not cold I would be thinking something is wrong with orifice tube for the front evaporator. I'm not sure of a good way to verify that on a split system because I'm not sure how the pressures will react.

Checking about makes it look like there's an orifice tube for the front A/C and an expansion block for the rear A/C. Figure out how that even works, 'cause I can't. Anyway, if the rear A/C is awesome, that indicates that the compressor/condenser/radiator fan are functional and there's at least a modicum of charge in the system. I suppose if the orifice tube was plugged then the front A/C wouldn't work worth jack but the rear would still work okay. Plugged orifice tube is usually because the compressor is self-destructing, but if you ever used A/C with sealant in it, that will happily plug an orifice tube as well if there is any moisture at all in the system, which is likely if you're servicing it with cans from Autozone instead of a proper A/C machine.

I'll stop before I get a rant going about sealant-contaminated refrigerant.

We replaced the orifice tube last fall. Or atleast I believe we did. Is it a cone shaped mesh filter looking thing in one of the lines? If so we definately replaced it.

FYI we used a proper A/C machine when vacuuming, and charging the system.

This. It all comes from one compressor with one charge of freon, so if the rear is cold its not a charge problem.

I'm not actually sure of that because i've experienced NUMEROUS times when an undercharged dual system would cool well in the front but not the rear, and correcting the refrigerant charge fixed it. I could imagine that a difference in plumbing/routing could cause the same situation but with a cold rear system and crappy front system.

In my wife's car an undercharge will get a cold passenger side and a tepid driver side.

In reply to Mazdax605:

Okay, cool, that answers a lot of questions and gives a good frame of reference.

Yes, that's the orifice tube. If it were in my shop, after messing with the blend door to make sure there a change in sound/temperature between cold and hot, I'd evacuate the system and see how much refrigerant was in it. If the charge level was good, I'd pop the orifice tube out to see if it were plugged up. If all THAT is good, I'd put it all back together and investigate the heater controls/motors/doors.

Other people would do the electronics first, which is fine, but IMO if you don't know you have a full charge in the system, you're flying blind. And the orifice tube is already somewhat suspect and is also a good canary in the coal mine with respect to crud in the system.

I was discussing this situation with my co-worker and he mentioned that two weeks ago, he was helping a friend with HIS Suburban, and his friend got a condenser for a front-A/C truck but his truck had dual A/C. Apparently dual A/C has the orifice tube in the line off the evaporator, but front-only has the orifice tube in the condenser. The new condenser came with an orifice tube pre-installed. So he accidentally had two orifice tubes in the system.

(edited for clarity)

Now the drivers side front is blowing warmish and the passenger side is blowing hot. Rear is still ice cold. I'm confused. I disconnected the battery to try to reset the system, but that doesn't seem to be the answer.

Chris

Now the front on both sides is just blowing face melting heat!!! berkeley this thing!!!

My 04 used to occasionally blow hot air with AC on but it seemed to me to be more of a controls issue as once I got it to stop blowing hot air the AC was always fine. It felt like the controller was opening the heater loop. I have a friend that works at Battles and also does side work at his house in Wareham if you want to have an expert look at it.

Yes, Chuck I would love to have an expert look at it. Or burn it. Either way I'm good. I punched the HVAC system this morning. Not one of my prouder moments.

This is starting to sound a lot like blend door issues.

In reply to gearheadmb:

Agreed... no matter how berked up the air conditioning is, it never makes the air get hotter than ambient... It's got to be a controls issue.

Is it all the front vents or just the two aimed at the driver? My 03 Burb does this. In my case, it is the blend door actuator on the bottom of the A/C box on the passengers side. I have dual zone climate control so there are two actuators to control each side. There is quite a bit of info on the web on this, showing how to fix it and where the actuators are.

Of course in my case the actuator isn't installed, the blend door shaft is broken and has a screw in it so it can be moved manually. Sucks driving in summer when that door decides to move on its own, and then getting blasted with warm air.

All the dash vents are blowing 1000 degree heat out of them, not just the two aimed at the driver. Even if taking it out of auto mode, it still has decided I want heat even though I've clearly turned the knobs to the left so that the display says 60* on each. I hate this climate control system, and have since I bought the truck 5+ years ago! Please just give me three knobs or slides attached to cables any day, thanks!

Did a hvac recalibration on the suburban this evening. Now only face melting heat on passengers side. Warmish on drivers side and cold in rear. I'm confused.

Sounds like the actuator(s) is going bad. They tend to crack one of the gears and then can't move the blend door all the way.

I have to wonder how any of this is better than the knobs or slide bars that were attached to cables for the hvac systems? I've never broken one of those. They still work perfectly in my 74 Mazda truck and 78 RX-7. Progress....

Mazdax605 wrote: I have to wonder how any of this is better than the knobs or slide bars that were attached to cables for the hvac systems?

Ease of assembly, takes up a lot less space, you can design the HVAC assembly for space efficient design instead of compromising it so that you can run cables to and fro, and you can't get computer control with a cable.

And another HUGE one is "haptics". People want all of the knobs and switches and dials to feel the same. You can't get that when one knob is a switch and another knob is moving a 2' long cable that is twisted into a figure 8.